Phonemes are the individual sounds we use
to make a language. There are 45 such sounds
in the English language, but other languages
have as many as 85.
Each single vowel and consonant in the alphabet
is a phoneme. In addition some letters have 2
sounds; the 'o' in 'hop' is a phoneme, and the 'o'
in 'hope' sounds different, so it is another phoneme.
The word 'purify' begins with a 'p' sound (a solitary
phoneme) but the 'u' letter could be pronounced
as in 'cute' or as in 'but' - two separate phonemes.
Some sounds can only be made by combining two
letters; 'sh' or 'th' for example, so each is a
phoneme.
The Welsh 'll' is a phoneme in the Welsh language,
but not in English. In Spanish, 'c' can be sounded
as in 'cat', but also as 'th' (cinco is pronounced as
'thinko' = five).
It's all a matter of knowing how letters sound in
each different language.
Thank heaven your boy is not learning Polish......